I am by no means an expert art historian but I'm not sure I 100% follow the logic of their conclusion.

"pentimenti, or correction marks, a common indication that “a painting is not a copy, but an original work created with artistic freedom.”"

How often are they analyzing copies made by 12 year old. Is a 12 year old more likely to have made errors or drifted from the source during the process of the copy? Could the corrections be attempts to bring the painting closer to its source, because it wasnt close enough?

If you're copying from another painting, you don't paint a figure and then decide to move it a centimeter to the left. But original paintings often have such changes.